1. Field of the Invention
This invention relates to automobile passenger restraints. More specifically, this invention relates to sensors for detecting low "g" accelerations and vehicle tilting for the purpose of activating or deactivating the primary automobile occupant restraint.
2. Description of Related Art
Automobile occupant restraints, including seat belts, airbags and belt tensioners, are important components of an automobile occupant safety system. It is essential, for the best performance of the restraint, to determine when vehicle acceleration or tilt exceeds a specified value. The acceleration or degree of tilt can indicate a collision or the existence of highly sloped terrain. Indications from such a sensor as this invention can be used to trigger an airbag or the tensioning of belt restraints.
A variety of tilt or acceleration sensors have been developed and are widely used in vehicles. A typical sensor for this application uses a mass known as the "standing man" which works with an optical pair. When the mass senses accelerations or tilt greater than a specified parameter, it tilts. This tilting lifts a leaver which then causes a break in the optical beam resulting in the activation or deactivation of the occupant restraint by a control module. Typically, such sensors have a relatively large number of supporting components and potential failure mechanisms. Such sensors require a relatively large amount of hands on assembly effort and associated quality checks.
A second type of sensor known in the industry is commonly referred to as a "Schmidt" sensor. This sensor is essentially the same as the previously described sensor, but has its components scaled down and placed in a single final assembly. While the same number of failure mechanisms are present, the assembly time and effort is improved from the typical sensor. Unfortunately, the manufacturing cost of the "Schmidt" sensor is much higher than the typical sensor.
Alternative sensors use displaceable bars or pivoting arms abutting against inertia bodies and operated by the movements of the bodies. It is also well known to use light rays or radiation from other radiating sources to sense or detect the position or movements of inertia bodies in locking devices for vehicle safety belts. It is particularly known to use light rays that can be reflected by a surface of an inertia body, for example a pendulum, where the reflected light rays being detected by a light sensitive means. When the inertia body changes position, the output from the light sensitive means is changed and this output is used as a control for the occupant restraint. One disadvantage of this type of sensing device is that to provide reliable operation the light radiating means and the light detecting means must be positioned with a high degree of accuracy in relation to the reflecting surface of the inertia body. Such accuracy is particularly difficult to achieve, when the inertia body is a standing, tiltable inertia means.
An alternative inertia member used to isolate the electric circuits of a motor vehicle in the event of an impact, is a double supported apertured pendulum member, which maintains a horizontal position as it swings, and which intercepts a light beam between a light source and a light sensor. The light beam normally passes through the aperture in the pendulum member. The light beam radiation received by a detector, through the aperture in the pendulum, provides an indication of the position of the inertia body.
Other safety system triggering or sensing apparatuses used for the protection of motor vehicle occupants include: a system employing a two sensors, one oriented substantially parallel to the forward direction of motion of the vehicle and a second oriented at an angle relative to the first axis, where the acceleration signals generated by the sensors are evaluated using digital and analog processors; an acceleration sensor that includes a permanent magnet mounted for movement within a cylindrical cavity in a body of non-magnetic material, where acceleration forces on the magnet move the magnet toward one of the ends of the cavity, results in a change in electrical conductance between electrical contacts within the cavity; an impact sensor including a permanent magnet disposed within a cavity and biased by magnetic force toward one end of the cavity, where the motion of the magnet in the cavity is sensed by a Weigan wire or Hall sensor; a sensor arrangement which responds to a longitudinal and/or transverse acceleration of the motor vehicle and which is configured to recognize a near weightless state of the vehicle as when the vehicle moves in a manner similar to free fall; an acceleration sensor that comprises a body of non-magnetic construction having a linear internal cavity of uniform cross section and a pair of permanent magnets movably mounted within the cavity, such that the magnets are urged to opposite ends of the cavity by the force of magnetic repulsion, where the sensor generates an output signal responsive to acceleration forces on either of the magnets which are sufficient to overcome the force of magnetic repulsion; a deceleration sensor comprising a sensor mass, a spring-loaded firing pin received in a guide bore, a trigger level for engaging the firing pin in a dormant sate until the trigger level is disengaged from the sensor mass as a result of the occurrence of a deceleration in excess of the threshold level and the resulting inertia motion of the sensor mass; and a deceleration sensor comprising a pair of sensor masses in the form of pendulums, a spring-loaded firing pin and a pair of trigger levels; a sensor having a gas-filled sealed tube having an inertial mass disposed in a closely fitting manner forming an annular orifice between the mass and the tube, where the mass is pre-loaded and biased and, upon the tube experiencing a level of velocity change above a predetermined amount, movement of the mass in the tube to activate the set of electrical contacts is damped by a viscous laminar flow of the gas through the annual orifice.
For general background material, the reader is directed to U.S. Pat. Nos. 3,981,518, 3,981,520, 4,097,699, 4,889,068, 4,955,638, 4,985,835, 5,132,662, 5,177,370, 5,261,506, 5,430,334, 5,449,198, 5,485,041, 5,620,203, and European Patent Application 0,179,120, each of which is hereby incorporated by reference in its entirety for the material disclosed therein.